The first step in trying to figure this out is to ask yourself why you suspect that she is cheating in the first place.

In other words, what particular acts or events led you to believe this. It is very important to do this because you must eliminate anything that is based out of emotional unhappiness.

The emotional unhappiness typically occurs when you start feeling insecure about your influence in the relationship. This often occurs when you feel like the relationship is not headed in the right direction.